1. Field of the Invention
The present invention relates to a magnetic head and a magnetic disk drive, or more particularly, to a magnetic head and a magnetic disk drive which are used for a shingled recording method.
2. Description of the Related Art
For increasing the storage capacity of a magnetic recording device represented by a hard disk drive, it is necessary to improve a recording density for information to be recorded in recording media. In order to improve the recording density, there is made an approach that the width of a recording track recorded in the medium is narrowed to increase a track density, or that a bit length on the recording track is shortened, that is, a linear recording density is increased. However, when the pole width of a recording head is narrowed in order to increase the track density, that is, in order to narrow the recording track width, the intensity of a recording magnetic field induced by the recording head is generally decreased, and a sufficient ability to write the recording media becomes unavailable.
Cited as a method for addressing the problem is a method called shingled recording. According to the shingled recording method, when a certain track is recorded, the track is recorded while being overwritten on one side of an adjoining recording pattern that is already recorded. Another recording track is formed while being overwritten on the same side of another recording pattern. As a result, an effective recording track width in the shingled recording method takes on a value obtained by subtracting the width of a portion, which is deleted while being overwritten with an adjoining track, from the width of a recording pattern formed by the recording head. Therefore, the shingled recording method obviates the necessity of matching the pole width of the recording head with the recording track width. This makes it possible to adopt the recording head whose pole width is larger than the effective recording track width. Therefore, even when the effective recording track width is diminished, a sufficient writing ability is available. As a result, a high track density can be realized, and a high areal density can be provided.
By the way, as far as a magnetic recording device represented by a hard disk drive is concerned, a gap is created between a head and a recording medium in order to prevent abrasion between the head and recording medium. A recording magnetic field induced by the magnetic poles of the recording head spatially spreads as long as the gap is present between the recording medium and recording head. Therefore, an inter-bit transition in a down-track direction of a recording track (a longitudinal direction of a record track, that is, a head advancing direction) does not appear straight in line with the shape of the recording head but is curved without fail. This is called a transition curvature.
In the shingled recording method, a one-side edge of a recording pattern that is recorded once is overwritten with an adjoining track in order to form an effective recording track. In other words, the recording method leaves a portion that has not been overwritten. Compared with an existing method in which the recording pattern is not overwritten, the magnitude of a curvature that occupies an effective recording track width gets larger. In addition, the transition curvature is always asymmetrical.
A typical reproducing head includes a sensor that senses a signal magnetic field induced from a recording medium, and a pair of magnetic shields that is formed to sandwich the sensor. In the reproducing head, the gap between the shields is formed to be parallel with a cross-track direction of a recording track (a direction intersecting a track, that is, a direction perpendicular to the down-track direction).
When the foregoing reproducing head is used to reproduce a recording track that has been recorded in a shingled manner, the shape of the shield-to-shield gap is deviated from a bit shape, which shows that an inter-bit transition is asymmetrically curved, due to the transition curvature and the fact that the recording track is overwritten on one side of a recording pattern. Therefore, a signal resolution in the down-track direction and a signal-to-noise ratio therein are degraded. This poses a problem in that a bit error rate increases.
A method of denting a trailing edge of a recording head which is disclosed in Japanese Patent Application Laid-Open Publication No. 2002-279606 and Japanese Patent Application Laid-Open Publication No. 2005-293693 proves effective in reducing a curvature. However, it is unfeasible to form a dent locally in the delicate recording head during a process of manufacturing the recording head, and to control the depth of the dent. Even if a transition curvature can be reduced by devising the shape of the trailing edge, as long as there is a gap between the recording head and a recording layer of a medium, since a magnetic field induced by the recording head spatially spreads, the transition curvature will not, in principle, be eliminated. The problem of an increase in a bit error rate due to the transition curvature remains unsolved.